Federal immigration enforcement agents raided 7-Eleven stores across the country early Wednesday, in search of employees who were in the U.S. illegally and managers who knowingly employed them.

Agents with U.S. Immigration and Customs Enforcement conducted sweeps of 98 stores in 17 states and Washington, D.C., arresting 21 people on suspicion of being in the country illegally.

“Today’s actions send a strong message to U.S. businesses that hire and employ an illegal workforce: ICE will enforce the law, and if you are found to be breaking the law, you will be held accountable,” Thomas D. Homan, ICE’s deputy director, said in a statement.

It’s the largest operation against a single employer since President Trump assumed office.

The sweeps come as ICE has stepped up arrests. From late January through August 2017, arrests were up more than 43 percent since the same period in 2016. But the agency deported fewer people in the 2017 fiscal year than in the year before, as NPR’s Laurel Wamsley notes, “because the group of people easiest to deport, those caught sneaking over the border illegally, dropped dramatically after Trump took office.”

Homan, ICE’s acting director, said immigration authorities are making an effort to target employers who hire unauthorized workers, in addition to the workers themselves.

“Businesses that hire illegal workers are a pull factor for illegal immigration and we are working hard to remove this magnet,” he said.

The Irving, Texas-based 7-Eleven said its stores are independently owned franchises and it was not responsible for hiring and verifying employment eligibility.

“As part of the 7-Eleven franchise agreement, 7-Eleven requires all franchise business owners to comply with all federal, state and local employment laws,” the company said in a statement. “This obligation requires 7-Eleven franchisees to verify work eligibility in the U.S. for all of their prospective employees prior to hiring. 7-Eleven takes compliance with immigration laws seriously and has terminated the franchise agreements of franchisees convicted of violating these laws.”

Advocates for limiting immigration applauded the decision to go after employers. “People come here to find work. If they can’t find work, they won’t come,” said Peter Nunez of the Center for Immigration Studies, which advocates stricter limits. “No one questions that the way to stop illegal immigration is to stop them from getting jobs.”

Authorities previously targeted 7-Eleven stores five years ago under the Obama administration, when New York prosecutors announced the arrest of nine people who operated stores in New York and Virginia, saying the owners obtained stolen Social Security numbers to put undocumented workers on the payroll. As WNYC’s Ilya Marritz reported at the time, “when 7-Eleven sent out wage checks, the store owners kept most of the money for themselves.”

ICE officials then blamed 7-Eleven for keeping poor track of its payroll system, which enabled the use of Social Security numbers for multiple people.

“Under President George W. Bush, ICE grabbed headlines by rounding up unauthorized workers at meatpacking plants, fruit suppliers, car washes and residences. In a shift, the agency under President Barack Obama focused on catching border crossers, deporting convicted criminals and pursuing employers on paper, by inspecting the I-9 forms that employers are required to fill out and keep to verify their workers’ eligibility.”

In 2008, authorities conducted some of the largest-ever workplace raids: In May, immigration agents arrested nearly 400 workers at a meatpacking plant in Postville, Iowa. Three months later, federal officials arrested about 600 workers at a manufacturing plant in Mississippi.

By 2013, during the second term of President Obama, the number of audits of employers doubled to more than 3,000 a year.

Critics said the Bush administration’s workplace raids “did not create a large deterrence and it did nothing to solve the problem of the many undocumented workers who remain here contributing to our economy and supporting their families,” Michael Kaufman of the American Civil Liberties Union told Gonzales.

Immigration policy has regained focus this week after President Trump held a meeting with lawmakers over the future of recipients of the Deferred Action for Childhood Arrivals program — young immigrants who were brought to the U.S. illegally as children. Trump called for a “bipartisan bill of love” to allow them to remain in the country after his administration rescinded the DACA program last year. He also said he was open to overhauling immigration policy on a larger level.